1. Field of the Invention
The present invention relates to a field emission planar lighting lamp and, more particularly, to a field emission planar lighting lamp with improved light utilization efficiency.
2. Description of Related Art
Field emission lighting lamps have advantages of simple structures, high brightness, and power saving, and can meet the requirements of flatness and large area. Hence, field emission lighting lamps are considered having potential for the displacement of fluorescent lamps.
FIG. 1 is a perspective view showing the operation principle of a conventional field emission lighting lamp. As shown in FIG. 1, the conventional field emission lighting lamp comprises: a cathode electrode 12, an electron emissive layer 14, an anode electrode 15, a phosphor layer 16, a front substrate 17, and a base substrate 11. The anode electrode 15 and the phosphor layer 16 are disposed on the front substrate 17, and the cathode electrode 12 and the electron emissive layer 14 are disposed on the base substrate 11. Hence, when a voltage is applied between the cathode electrode 12 and the anode electrode 15, an electric field is formed between the cathode electrode 12 and the anode electrode 15 to induce a tunnel effect. When the tunnel effect occurs, electrons release from the electron emissive layer 14, and the voltage applied on the anode electrode 15 accelerates the released electrons. Then, the accelerated electrons strike the phosphor layer 16 to excite the phosphor emitting light.
According to the conventional field emission lighting lamp, the front substrate 17 is generally a transparent glass substrate, and the material of the anode electrode 15 is a transparent conductive material such as ITO. Hence, when electrodes strike the phosphor layer 16, the light emitting from the phosphor layer 16 has to sequentially penetrate through the phosphor layer 16, the anode electrode 15, and the front substrate 17 to transmit to the outside. However, the electrons usually only strike the phosphor on the surface 161 of the phosphor layer 16, so the highest luminous efficiency would be found around the surface 161 of the phosphor layer 16. Hence, most of the light emitted from the phosphor layer 16 is restricted within the device and cannot be transmitted to the outside. In addition, partial light emitted from the surface 161 of the phosphor layer 16 may be absorbed by the phosphor layer 16, and partial reflective light cannot penetrate through the phosphor layer 16, the anode electrode 15, and the front substrate 17 to transmit outward. Therefore, the light extraction efficiency may further be reduced. Hence, the aforementioned conventional field emission lighting lamp generally has the disadvantage of low luminous efficiency.